1. Field of the Invention
The invention relates to a vacuum die-casting system, as well as to a method for operation of a vacuum die-casting system.
2. Description of the Related Art
Vacuum die-casting is known for the production of cast pieces made of metals and metal alloys, particularly of alloys of the metals Al, Mg, Zn, and Cu. Corresponding systems for vacuum die-casting are described, for example, in DE 4312647 A1, DE 102004057324 A1, or DE 102006010560 A1.
Vacuum die-casting is particularly used where great demands are made on the sealing ability, elongation to fracture, strength and weldability of the cast parts. A high quality of the cast parts is achieved by means of vacuum die-casting, because less air and gases are enclosed in the material. This is particularly true for cast parts made of aluminum or an aluminum alloy, which are still heat-treated or welded in a subsequent method step.
Aside from the use of liquid metals or metal alloys, there are various special methods in vacuum die-casting, such as those described in “Rolf Roller (ed.): Fachkunde für Gieβereitechnische Berufe [Technical knowledge for foundry technology professions], Haan-Gruiten, 2007; pages 186-187.” The present invention also comprises such special methods, to the extent that the corresponding vacuum die-casting systems have a casting chamber having a filling opening, a casting piston that can move in the casting chamber, and a piston rod, whereby the latter connects the casting piston with a casting drive, and whereby a ring gap is formed between the outer mantle of the casting piston and the inner wall of the casting chamber, which gap usually forms a leak site—as described below.
In vacuum die-casting, it is known that a partial vacuum or vacuum is produced in the mold cavity of the vacuum die-casting system, after the casting chamber has been filled with casting melt and the casting piston has moved past the filling opening of the casting chamber.
Tn order to bring the partial vacuum produced in the mold cavity of the casting mold or in the casting chamber connected with the mold cavity to a minimum during vacuum die-casting, is necessary to seal off all possible leaks or defects within the complete vacuum system, to the greatest possible extent.
An extremely important leak site, in this connection, is the ring gap between the inner wall of the casting chamber and the outer mantle of the casting piston. At this leak site, gases that penetrate from the back side of the casting piston actually foam up the casting melt in the casting chamber, which is under vacuum, and produce a gas porosity in the cast part that minimizes or excludes heat treatment and weldability.
DE 43 12 647 A1 offers a solution for closing this leak site, according to which a very complicated slide sleeve that can be evacuated is pushed over the casting chamber system or casting piston system, in order to produce a vacuum behind the piston. In this connection, the very great maintenance effort of such vacuum die-casting systems is particularly disadvantageous.